Hydraulic drive vehicle

ABSTRACT

A vehicle includes a first transaxle incorporating a first hydraulic motor for driving a first axle, a pair of second transaxles incorporating respective second hydraulic motors for driving respective second axles, and a pump housing separated from the first transaxle and the pair of second transaxles. The pump housing incorporates a hydraulic pump. The first hydraulic motor and the pair of second hydraulic motors are fluidly connected in series to the hydraulic pump. The second hydraulic motors are fluidly connected in parallel to the hydraulic pump.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.11/033,543, filed Jan. 12, 2005, which is a divisional of U.S.application Ser. No. 10/270,978, filed Oct. 15, 2002, now U.S. Pat. No.6,845,837, the entire disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a transaxle apparatus having a housing whichincorporates a hydrostatic transmission (HST) and a hydraulic actuatorarranged outside the housing which can be supplied with hydraulic fluidfrom the HST. More particularly, it relates to a four-wheel-drivearticulated working vehicle.

2. Related Art

A well-known articulated riding lawn mower has first and second frameswhich are mutually pivotally coupled at proximal ends thereof so as toturn relatively to each other around a vertically axial pivot steeringoperation (i.e., manipulation of a steering wheel). The first frame isequipped with a prime mover and a transaxle apparatus which supportsfirst axles driven by power from the prime mover. The second frame isequipped with a working device such as a mower device, an operatingsection, and an axle casing that supports second axles freely rotatably.

In the Japanese Patent Laid Open Gazette 2000-270651, for example, isdisclosed an articulated four-wheeled lawn mower, which includes as thefirst frame a rear frame and as the second frame a front frame. On therear frame, a hydrostatic transmission (hereinafter, “HST”) is disposed,which transfers engine power to rear wheels supported by the rear frame.Moreover, in the rear frame is disposed a power take-off shaft, whichreceives power from a pump shaft of a hydraulic pump of the HST. Thepump shaft revolves synchronously to the engine power output revolution.The revolution of the pump shaft is transferred to the mower devicesupported by the front frame.

Generally, as to each of vehicles having the above structure, while thefirst axles supported by the transaxle apparatus of the first frame(usually serving as a rear frame) is driven by the prime mover, thesecond axles supported by the axle casing of the second frame (usuallyserving as a front frame) revolve freely and not in driving associationwith the power for driving the axles of the first frame. Thus, thevehicle is a so-called two-wheel drive vehicle.

However, while the two-wheel-drive vehicle which drives only rear wheelsexhibits superior steering performance, it lacks stability when workingon a slope and roadability when running on a bad road. Further, if thevehicle is an articulated vehicle, the steering performance must beimproved because the vehicle is bent at the coupling part of the frames.Moreover, the vehicle is difficult to bail out if it becomes stuck, suchas in mud, etc.

For solving these problems, a four-wheel-drive design, which drives bothfront and rear wheels, is desirable for the articulated vehicle. Therear frame of the vehicle disclosed in the above document is providedwith an HST and a power take-off shaft for transferring power to theworking device. However, as mentioned above, since the power take-offshaft revolves synchronously with the revolution of the pump shaft, therotary speed of the pump shaft is fixed as long as the engine speed isfixed. On the other hand, the rotary speed of the rear wheels, which aredriven by the power output of the hydraulic motor, is changed variablyby a running speed changing operation which adjusts the angle of amovable swash plate of the hydraulic pump. Therefore, the power take-offshaft for driving the working device cannot be used as a front wheeldrive shaft. Even if another power take-off shaft for front-wheel-drive,whose rotation is synchronized with the power output of the HST for rearwheel drive, can be connected to the transaxle apparatus mounted in therear frame, severe limitations exist for such an arrangement to infixadditional mechanical transmission system between front and reartransaxle apparatuses, because the turning of front and rear frames mustbe permitted, as well as infixing the transmission system for theworking device drive therebetween.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide on an articulatedvehicle a transaxle apparatus for making the articulated vehicle afour-wheel-drive articulated working vehicle. The transaxle apparatusincludes a housing containing an HST and is enabled to supply hydraulicfluid from the HST to a hydraulic actuator arranged outside of thehousing.

To achieve the first object, according to the transaxle apparatus of thepresent invention, a housing containing an HST is provided. The HSTcomprises a hydraulic pump receiving power from the prime mover, ahydraulic motor driven in response to fluid from the hydraulic pump todrive first axles, and a center section. In the center section areprovided fluid passages, which are disposed in the housing so as tobring the hydraulic pump and the hydraulic motor into mutual fluidalconnection. Also disposed in the center section are ports, which arelocated on an outer surface of the housing and fluidly connected withthe fluid passages so as to introduce fluid flowing in the fluidpassages into a hydraulic actuator disposed outside the housing. An axledriven by the hydraulic motor is disposed in the housing.

The hydraulic actuator may comprise a hydraulic motor for driving asecond axle disposed outside the housing so as to constitute afour-wheel-drive vehicle.

The center section is detachably attached to the housing, therebyadvantageously facilitating its manufacture and preventing fluid fromleaking from the fluid passages to the outside of the housing.

The ports are equipped with tubular elements for supplying pressurizedfluid (hydraulic fluid) to the hydraulic actuator (the hydraulic motor)arranged outside the housing. The housing is equipped with openings forexposing the utmost ends of the tubular elements outside the housing.Furthermore, the tubular elements are detachably attached to the centersection.

Accordingly, flexibility of the arrangement of the elements forsupplying pressurized hydraulic fluid from the center section in thehousing to the outside of the housing in relation to other components(for example, means for transmitting power from the prime mover to aworking device) arranged between the first and second frames can beenhanced. Moreover, inexpensive parts such as a fluid hose can be usedfor the tubular elements. Since the tubular elements are easilydetached, they facilitate maintenance. Furthermore, removal of thetubular elements can change the vehicle into two-wheel-drive vehicle.

Moreover, the above-mentioned ports of the transaxle apparatus fluidlyconnect in parallel the hydraulic motor in the housing and the hydraulicmotor outside of the housing to the hydraulic pump in the housing. Thisstructure is suitable for a vehicle which is designed so that, when thevehicle turns, distances from a turning center of the vehicle to thefront and rear axles, namely, to the first axle in the housing and thesecond axle out of the housing, are different from each other so as tocause a rotary speed difference between the front and rear axles. Inthis structure, pressurized hydraulic fluid discharged from thehydraulic pump is distributed to both of the hydraulic motors, insideand outside of the housing, in correspondence to the rotary speeddifference between the axles.

Alternatively, the ports of the transaxle apparatus may fluidly connectin series the hydraulic motor in the housing and the hydraulic motoroutside of the housing to the hydraulic pump in the housing. Thisstructure is suitable for a vehicle designed so that, when the vehicleturns, distances from the turning center of the vehicle to the front andrear axles, namely, to the first axle in the housing and the second axleoutside of the housing, are substantially equal to each other so as notto cause a rotary speed difference between the front and rear axles.According to the series connection structure compared with theabove-mentioned parallel connection structure, the entire amount offluid discharged from the hydraulic pump is supplied to the hydraulicmotor in the housing and the hydraulic motor outside of the housing aslong as the hydraulic pump is revolving. Thus, even if either of thefront or rear wheels gets stuck, as in mud, etc., and the front or rearaxle driven by one of the hydraulic motors idles, the other hydraulicmotor drives the other axle using all of the fluid discharged by thehydraulic pump, and the vehicle can be freed.

In another embodiment, a vehicle includes a first transaxleincorporating a first hydraulic motor for driving a first axle, a pairof second transaxles incorporating respective second hydraulic motorsfor driving respective second axles, and a pump housing separated fromthe first transaxle and the pair of second transaxles and incorporatinga hydraulic pump. The first hydraulic motor and the pair of secondhydraulic motors are fluidly connected in series to the hydraulic pump.The second hydraulic motors are fluidly connected in parallel to thehydraulic pump.

A second object of the present invention is to provide afour-wheel-drive articulated working vehicle with the above-mentionedtransaxle apparatus, including first and second frames, each of whichhas opposite proximal and distal ends with respect to the vehicle. Thefirst and second frames are coupled mutually at the proximal endsthereof so as to be rotated in relation to each other around avertically axial pivot in the coupling part therebetween by a steeringoperation. A prime mover is mounted on the first frame, and a workingdevice is attached to the distal end of the second frame.

To achieve the second object, according to the vehicle of the presentinvention, the transaxle apparatus including the HST for supporting anddriving a pair of first axles serves as a first transaxle apparatussupported by the first frame on which the prime mover is mounted. Thehydraulic motor disposed in the housing of the first transaxle apparatusserves as a first hydraulic motor. A second transaxle apparatus with asecond hydraulic motor, which supports and drives a pair of secondaxles, is supported by the second frame provided on the distal endthereof with the working device. The second hydraulic motor is fluidlyconnected to the above-mentioned ports of the center section of the HSTdisposed in the first transaxle apparatus. As means for receiving powerfrom the prime mover, a rotor is disposed at the junction between thefirst and second frames so as to locate a rotation axis of the rotor onthe vertical axial pivot. The lengths of the pair of second axles aredifferent from each other, and a transmission element for drivinglyconnecting the prime mover to the working device crosses the longer thepair of second axles.

Due to the above structures, fluid connection of the HST of the firsttransaxle apparatus to the second hydraulic motor can be ensured withoutinterfering with the transmission system from the prime mover to theworking device, thereby realizing a four-wheel-drive articulated workingvehicle.

Moreover, the four-wheel-drive articulated working vehicle is designedso that distances from the vertically axial pivot in the coupling partto an axis of the first axles and to an axis of the second axles aresubstantially equal to each other. The vehicle can be simplified byapplying the series fluid connection as the fluid connection of thefirst and second hydraulic motors through the ports to the hydraulicpump. Accordingly, the entire amount of fluid discharged from thehydraulic pump is supplied to each of the first and second hydraulicmotors as long as the hydraulic pump is revolving. Thus, even if one ofthe drive wheels gets stuck, as in mud, etc., and either the first orsecond axles driven by one of the hydraulic motors idles, the otherhydraulic motor drives the other axles using the entire amount of fluiddischarged from the hydraulic pump so that the vehicle can be freed.

These and other objects, features, and advantages of the invention willbecome more apparent upon a reading of the following detaileddescription and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

FIG. 1 is a side view of a riding lawn mower as an embodiment of afour-wheel-drive articulated working vehicle according to the presentinvention.

FIG. 2 is a plan view partly in section of the vehicle of FIG. 1.

FIG. 3 is a rear view partly in section of a front transaxle apparatusprovided in the vehicle of FIG. 1.

FIG. 4 is a plan view of the front transaxle apparatus of the presentinvention from which an upper housing half is removed.

FIG. 5 is a fragmentary rear view partly in section of the fronttransaxle apparatus of the present invention, showing a hydraulic motordisposed therein.

FIG. 6 is a sectional left side view of the front transaxle apparatus ofthe present invention.

FIG. 7 is a right side view of a rear transaxle apparatus.

FIG. 8 is a plan view partly in section of the rear transaxle apparatusaccording to the first embodiment of the present invention from which anupper housing half is removed, showing that a center section havingports for series connection is disposed therein.

FIG. 9 is a rear view partly in section of the rear transaxle apparatusaccording to the first embodiment.

FIG. 10 is a fragmentary sectional plan view of the rear transaxleapparatus according to the first embodiment, showing the fluid passagestructure formed in the center section disposed therein.

FIG. 11 is a fragmentary sectional side view of the rear transaxleapparatus according to the first embodiment of the present invention.

FIG. 12 is a hydraulic circuit diagram showing the hydraulic motor ofthe rear transaxle apparatus according to the first embodiment of thepresent invention and the hydraulic motor of the front transaxleapparatus are fluidly connected to the hydraulic pump of the reartransaxle apparatus in series.

FIG. 13 is a hydraulic circuit diagram of the motor of FIG. 12, showinga case where the hydraulic motor of the front transaxle apparatus isexchanged for a variable displacement type.

FIG. 14 is a plan view partly in section of a rear transaxle apparatusaccording to a second embodiment of the present invention from which anupper housing half is removed, showing that a center section havingports for parallel connection is disposed therein.

FIG. 15 is a rear view partly in section of a portion of the reartransaxle apparatus according to the second embodiment where a thirdpassage is passed.

FIG. 16 is a rear view partly in section of another portion of thetransaxle of FIG. 15 where a fourth passage is passed.

FIG. 17 is a fragmentary sectional plan view of the rear transaxleapparatus according to the second embodiment, showing fluid passagestructure formed in the center section.

FIG. 18 is a fragmentary sectional side view of the rear transaxleapparatus according to the second embodiment.

FIG. 19 is a hydraulic circuit diagram showing the hydraulic motor ofthe rear transaxle apparatus according to the second embodiment and thehydraulic motor of the front transaxle apparatus are fluidly connectedin parallel to the hydraulic pump of the rear transaxle apparatus.

FIG. 20 is a plan view partly in section of a four-wheel-drivearticulated working vehicle in which front transaxle apparatuses havingrespective hydraulic motors are provided to right and left front wheels,respectively.

FIG. 21 is a rear view partly in section of the right and left fronttransaxle apparatuses provided to the working vehicle.

FIG. 22 is a plan view partly in section of the front transaxleapparatuses 400R (400L) provided to the working vehicle.

FIG. 23 is a hydraulic circuit diagram showing that a hydraulic motor ofthe rear transaxle apparatus according to the first embodiment of thepresent invention and a circuit which fluidly connects hydraulic motorsof both the front transaxle apparatuses to each other in parallel arefluidly connected in series to the hydraulic pump of the rear transaxleapparatus.

FIG. 24 is a hydraulic circuit diagram of the present invention in acase that variable displacement hydraulic motors serve as both thehydraulic motors.

FIG. 25 is a hydraulic circuit diagram showing the hydraulic motor ofthe rear transaxle apparatus according to the first embodiment and thehydraulic motors of both the front transaxle apparatuses are fluidlyconnected in series to the hydraulic pump of the rear transaxleapparatus.

FIG. 26 is a hydraulic circuit diagram showing the hydraulic motor ofthe rear transaxle apparatus according to the second embodiment of thepresent invention and the hydraulic motors of both the front transaxleapparatuses are fluidly connected in parallel to the hydraulic pump ofthe rear transaxle apparatus.

FIG. 27 is a hydraulic circuit diagram showing the hydraulic motor ofthe rear transaxle apparatus according to the second embodiment of thepresent invention and a circuit, which fluidly connects in series thehydraulic motors of both the front transaxle apparatuses to each other,are fluidly connected in parallel to the hydraulic pump of the reartransaxle apparatus.

FIG. 28 is a hydraulic circuit diagram of a (articulated)four-wheel-drive working vehicle equipped with separate left and rightfront transaxles and a pump unit separated from a rear transaxle,wherein all hydraulic motors are fixed in displacement.

FIG. 29 is a hydraulic circuit diagram of a (articulated)four-wheel-drive working vehicle equipped with separate left and rightfront transaxles and a pump unit separated from a rear transaxle,wherein a hydraulic motor in the rear transaxle is variable indisplacement.

FIG. 30 is a hydraulic circuit diagram of a (Ackerman type steering)four-wheel-drive working vehicle equipped with separate left and rightfront transaxles and a pump unit separated from a rear transaxle,wherein hydraulic motors in the respective front transaxles are variablein displacement.

DETAILED DESCRIPTION OF THE INVENTION

Description will be given of a four-wheel-drive articulated workingvehicle according to the present invention.

FIGS. 1 and 2 show a working vehicle equipped at a front portion thereofwith a mower device 3 serving as a working device. A front frame 11 isprovided with a front transaxle apparatus from which front wheel axles12L and 12R are extended in a transverse direction and fixed torespective front wheels 13. A rear frame 21 is provided with a reartransaxle apparatus from which rear wheel axles 22L and 22R are extendedin a transverse direction and fixed to respective rear wheels 23.

A rear end portion of the front frame 11 is horizontally rotatablycoupled to a front end portion of the rear frame 21 through a couplingpart 50. Coupling part 50 constitutes a pivot point of rotation of boththe frames. Thus, the working vehicle including the horizontallyturnable front and rear frames 11 and 21 is bendable at the intermediateportion thereof, thereby being a so-called articulated vehicle.

A steering column 14, a steering wheel 4, and a pedal 15 are arranged ina front portion of front frame 11, and a seat 9 is disposed behindsteering column 14, thereby constituting an operation part 16 on frontframe 11. Mower device 3 is vertically movably provided at a distal endof front frame 11, that is, at a downwardly forward position fromoperation part 16. Mower device 3 is driven by an engine 5.

As shown in FIGS. 1 and 2, on rear frame 21 is disposed engine 5 coveredwith a bonnet 8. A rear transaxle apparatus is arranged under engine 5.

On the rear frame 21 end, a first engine output pulley 94 is fixed to anoutput shaft 93 of engine 5, an HST input pulley 292 is fixed to a pumpshaft 231 of a hydraulic pump incorporated in the rear transaxleapparatus, and a second engine output pulley 96 (shown in FIG. 1) isfixed to output shaft 93 under first engine output pulley 94.

On the front frame 11 end, a working device drive power input pulley 111is fixed to a power input shaft 112 of mower device 3 as a workingdevice, and an idle pulley 98 is rotatably supported through a bearing(not shown) on a support shaft 97 suspended from front frame 11.

Moreover, as shown in FIGS. 1 and 2, regarding coupling part 50, acylindrical pivotal connector 28 is disposed on the laterally middlefront end of rear frame 21 and not-relatively rotatably supports a jointshaft 55 in the vertical direction. A platy pivotal connector 18, whichis U-shaped in side view, is pivotally coupled to joint shaft 55. Thus,rear frame 21 and front frame 11 are pivotally coupled so as to behorizontally turnable. In this way, pivotal connectors 18 and 28 areprovided at the respective proximal ends of frames 11 and 21, each ofwhich faces to the proximal side of the vehicle, and are pivotallyconnected to each other through joint shaft 55 so as to constitutecoupling part 50. Thus, both frames 11 and 21 are arranged in tandem andcoupled so as to be turnable around joint shaft 55, thereby enabling thevehicle to be steered.

A lower end of joint shaft 55 is extended below pivotal connector 18 soas to support a power output pulley 57 and a power input pulley 56rotatably thereon through bearings (not shown).

As shown in FIGS. 1 and 2, on rear frame 21 end, a rear drivetransmission belt 92 is wound around the first engine output pulley 94and HST input pulley 292, and a first working-device drive transmissionbelt 58 is wound around the second engine output pulley 96 and powerinput pulley 56.

On front frame 11 end, second working-device drive transmission belt 59is wound around an idle pulley 98 (FIG. 2), a working-device drive powerinput pulley 111, and power output pulley 57.

Due to this construction, engine output is transmitted to HST inputpulley 292 through rear drive transmission belt 92 from first engineoutput pulley 94 so as to rotate pump shaft 231. The engine output isalso transmitted to working-device drive power input pulley 111 throughsecond engine output pulley 96, first working-device drive transmissionbelt 58, power input pulley 56, power output pulley 57 integrallyrotating power input pulley 56, and second working-device drivetransmission belt 59, so as to rotate a power input axis 112, therebyrotating mowing blades 17.

As shown in FIG. 2, at a position shifted leftward from lateral middleof front frame 11 is disposed front transaxle apparatus, which supportsleft and right front wheel axles 12R and 12L so as to extend right frontwheel axle 12R longer than left wheel axle 12L.

As shown in FIGS. 2 and 3, a pair of left and right collars 99 a and 99b are freely rotatably on right front wheel axle 12R at a substantiallylaterally middle position of front frame 11. The lower surfaces ofsecond working-device drive transmission belt 59 comes into contact withthe respective upper surfaces of collars 99 a and 99 b.

Hence, front transaxle apparatus supports the pair of axles whoselengths are different from each other, and second working-device drivetransmission belt 59, serving as a transmission element for drivinglyconnecting engine 5 and mower device 3 to each other, crosses the longeraxle of the pair; in other words, second working-device drivetransmission belt 59 changes direction by contacting collars 99 a and 99b on the longer axle.

In this way, second working-device drive transmission belt 59 passesabove front wheel axle 12R so as not reduce the road clearance.Moreover, since collars 99 a and 99 b are idled, second working-devicedrive transmission belt 59 is not damaged by friction.

Next, description will be given of the front transaxle apparatus. Asshown in FIG. 6, an upper housing half 46 and a lower housing half 47are vertically joined to each other so as to form one housing, whichprovides the external appearance of the front transaxle apparatus 10 andcontains within its interior a fluid sump and for incorporating thehydraulic motor, etc.

As shown in FIG. 4, a counter shaft 139, on which a reduction-gear train135 is freely provided, divides the hollow interior of the housing intoa first chamber 10 a, which incorporates a differential gear unit 120,and a second chamber 10 b, which incorporates a hydraulic motor 40.Driving force of hydraulic motor is transmitted to differential gearunit 120 through reduction-gear train 135.

As shown in FIG. 5, hydraulic motor is integrally disposed within fronttransaxle apparatus. On a vertical portion of center section 62 isformed a motor mounting surface 63 m (shown in FIG. 16) on which acylinder block 43 is rotatably and slidably supported. A plurality ofpistons 42 are reciprocally movably fitted through respective biasingsprings into a plurality of cylinder bores in cylinder block 43. Athrust bearing 44 a of a fixed swash plate 44 abuts against the heads ofpistons 42. An opening 44 b is provided in the center of fixed swashplate 44 so as to allow motor shaft 41 to pass therethrough. Fixed swashplate 44 is fixedly sandwiched between upper housing half 46 and lowerhousing half 47.

Motor shaft 41 is rotatably supported by a sealed bearing 45 held on thejoint surface between upper housing half 46 and lower housing half 47.Motor shaft 41 is not-relatively rotatably engaged with cylinder block43 so as to be disposed horizontally on the rotary axis of cylinderblock 43 and serve as an output shaft. In this way, front transaxleapparatus 10 contains an axial piston type hydraulic motor 40.

Moreover, as shown in FIG. 6, a pair of first and second kidney-ports 62a and 62 b are formed in motor mounting surface 63 m formed on thevertical portion of center section 62. First and second kidney-ports 62a and 62 b are connected to, respectively, horizontal first and secondfluid passages 53 a and 53 b bored within center section 62. As shown inFIG. 4, first fluid passage 53 a and second fluid passage 53 b areconnected to respective caps 54 a and 54 b to which hydraulic hoses areconnected. Thus, hydraulic motor 40 is fluidly connected to hydraulicpump 30 through hydraulic hoses (not shown).

As shown in FIG. 5, a bypass operation lever 65 for opening first fluidpassage 53 a and second fluid passage 53 b to the fluid sump is disposedabove upper housing half 46 in order to enable the axles (12L and 12R)to idle when the vehicle is towed. Bypass operation lever 65 is fixed ata basal portion thereof to an upper end of a vertical bypass lever shaft66 rotatably supported by an upper wall of upper housing half 46. Bypasslever shaft 66 extends at a lower end thereof to the interior of centersection 62 so as to be horizontally slidably in center section 62. Aflat surface 66 a is formed in a lower end side of bypass lever shaft 66so as to contact an end face of a push pin 67 which is allowed tocontact the rotationally sliding surface of cylinder block 43.

As shown in FIG. 6, a feeding-and-discarding port 46 a is formed in theupper portion of upper housing half 46 so as to enable hydraulic fluidto be fed or discharged from and to a reservoir tank (not shown).

As shown in FIGS. 4 and 5, a drive output gear 131 is fitted with splineonto an end of motor axis 41 opposite to center section 62 so as to berotated integrally with motor shaft 41. On the side of drive output gear131 facing section 62 is integrally formed a brake rotor 133 whosediameter is larger than that of drive output gear 131. Brake rotor 133is sandwiched between brake pads 134 a and 134 b (FIG. 4) so as to brakerotating motor shaft 41.

As shown in FIG. 4, a counter shaft 139 is arranged parallel to motorshaft 41, a wide, small diameter gear 137 fits loosely on counter shaft139, and a large diameter gear 136 is engaged with a toothed sideportion of small diameter gear 137, thereby forming reduction-gear train135.

Regarding reduction-gear train 135, while large diameter gear 136engages with drive output gear 131, small diameter gear 137 engages witha ring gear 121 of differential gear unit 120, thereby transmittingdriving force of motor shaft 41 to differential gear unit 120 throughreduction-gear train 135.

Moreover, differential gear unit 120 comprises ring gear 121, whichengages with small diameter gear 137 of reduction-gear train 135,pinions 123, which are rotatably supported by respective pinion shafts122 which project inward from an inner periphery of ring gear 121, andside gears 124 fixed to respective front wheel axles 12L and 12R andlaterally engaged with each of pinions 123. Due to this construction,the driving force from motor shaft 41 is transmitted to front wheelaxles 12L and 12R through reduction-gear train 135, ring gear 121,pinions 123, and side gears 124.

As shown in FIGS. 4 and 5, an end of motor axis 41, which is opposite tocylinder block 43, is extended outside of the housing so as to befixedly provided thereon with a cooling fan 191 for cooling fluidcollected in the front transaxle apparatus.

Description will now be given of the rear transaxle apparatus. As shownin FIG. 2, hydraulic motor 40 incorporated in front transaxle apparatus10, which drives front wheel axles 12L and 12R, is fluidly connectedthrough hydraulic hoses 81 a and 81 b to a hydraulic motor incorporatedin the rear transaxle apparatus 20, which drives rear wheel axles 22Land 22R.

As shown in FIGS. 8 and 9, rear transaxle apparatus comprises a housingwhich is formed by an upper housing half and a lower housing half 247vertically separably joined to each other so as to form a hollowinterior into which the hydraulic motor, etc., is incorporated.

The housing forms a bearing portion for a later-discussed motor shaft241 on the joint surface thereof between housing halves 246 and 247, andforms a bearing portion for journaling rear wheel axles 22L and 22R inthe upper housing half above the joint surface. Rear wheel axles 22L and22R are differentially connected at inner ends thereof to each otherthrough a differential gear unit 220, and extended outward fromrespective left and right outside walls of the housing.

As shown in FIG. 8, rear transaxle 20 apparatus is integrally formedtherein with an internal wall 248 which divides the inner space of reartransaxle 20 apparatus into first and second chambers 20 a and 20 b. Infirst chamber 20 a is disposed an HST 290, and in second chamber 20 bare disposed a drive train 249 comprising a gear train which transmitspower to differential gear unit 220 from motor shaft 241, differentialgear unit 220, and inner side ends of rear wheel axles 22L and 22R.

Internal wall 248 comprises a longitudinal portion parallel to rearwheel axles 22L and 22R, and a perpendicular portion extendedperpendicularly to the longitudinal portion. These two portions areprovided continuously so as to arrange first chamber 20 a adjacent tosecond chamber 20 b. An upper wall portion of internal wall 248 extendsdownward from an inner upper wall surface of upper half housing 246, anda lower portion of internal wall 248 rises from the inner bottom surfaceof lower half housing 247 through the joint surface. By joining upperand lower housings 246 and 247, end faces of both the upper and lowerwall portions are also joined to each other so as to form internal wall248, thereby dividing the inner space into first and second chambers 20a and 20 b which are independent of each other.

In the housing, first chamber 20 a is disposed in front of rear wheelaxle 22R and on a lateral side of drive train 249 which transmits powerto differential gear unit 220 from motor shaft 241.

In first chamber 20 a is detachably settled a center section 260 of theHST. A longitudinal portion of center section 260 is extendedrectangularly to rear wheel axles 22L and 22R, and a vertical surface isformed on a front portion of the longitudinal portion so as to serve asa motor mounting surface 260 m, onto which the hydraulic motor ismounted. A horizontal surface is formed on the rear portion of centersection 260 so as to serve as a pump mounting surface 260 p, onto whichthe hydraulic pump is mounted. In the center of pump mounting surface260 p is vertically supported a pump shaft 231.

Description will now be given of the hydraulic pump arranged on centersection 260.

As shown in FIG. 9, a cylinder block 233 is rotatably and slidablydisposed on pump mounting surface 260 p which is formed at thehorizontal portion of center section 260.

Pistons 232 are reciprocally movably fitted through respective biasingsprings into a plurality of cylinder bores in cylinder block 233. Athrust bearing 234 a of a movable swash plate 234 abuts against theheads of pistons 232. An opening 234 b is provided at the center ofmovable swash plate 234 so as to allow a pump shaft 231 to passtherethrough. A control arm 238 engages with a side of movable swashplate 234 so that a tilt angle of movable swash plate 234 is adjusted byrotating a control shaft 237 serving as a rotary shaft of control arm238.

In order that pump shaft 231 may function as an input shaft, pump shaft231 is rotatably supported by a bearing 235 engaged in an opening 236formed above first chamber 20 a in upper half housing 246 and isnot-relatively rotatably engaged with cylinder block 233, thereby beingarranged vertically on the rotary axis of cylinder block 233.

In this way, an axial piston type variable displacement hydraulic pumpis constructed in rear transaxle apparatus.

As shown in FIG. 9, the upper end of pump shaft 231 projects outwardlyfrom the rear transaxle apparatus. An HST input pulley 292 and a coolingfan 291 are fixed onto the upper end of pump shaft 231. Thus, whilecooling the hydraulic fluid accumulated in rear transaxle apparatus 20by cooling fan 291, driving force of the engine is inputted into HSTinput pulley 292 through a transmission element so as to rotate pumpshaft 231.

Description will now be given of the hydraulic motor 240 arranged oncenter section 260.

As shown in FIG. 8, a cylinder block 243 is rotatably and slidablydisposed on motor mounting surface 260 m which is formed at the verticalportion of center section 260.

A plurality of pistons 242 are reciprocally movably fitted into aplurality of cylinder bores in cylinder block 243 through respectivebiasing springs. The heads of pistons 242 abut against a thrust bearing244 a of a fixed swash plate 244 which is fixedly sandwiched betweenupper housing half 246 and lower housing half 247. An opening 244 b isprovided in the center of fixed swash plate 244 so as to allow motorshaft 241 to pass therethrough.

In order that motor shaft 241 may function as an output shaft, motorshaft 241 is rotatably supported by a sealed bearing 245 sandwichedbetween upper housing half 246 and lower housing half 247, and isnot-relatively rotatably engaged with cylinder block 243, thereby beingarranged horizontally on the rotary axis of cylinder block 243.

In this way, an axial piston type fixed displacement hydraulic motor isconstructed in rear transaxle apparatus 20.

Moreover, as shown in FIG. 8, the end portion of motor shaft 241opposite to center section 260 is fitted with a drive output gear 212 inspline fitting such that drive output gear 212 rotates with motor shaft241. The portion of motor shaft 241 outward from drive output gear 212is fitted with a brake rotor 213 in spline fitting. By pressing brakerotor 213 between brake pads 214 a and 214 b, rotating motor shaft 241is braked. In this embodiment, as mentioned above, brake devicesincluding brake rotor 213 are provided in respective transaxleapparatuses 10 and 20, although it may be considered that at least oneof transaxle apparatuses 10 and 20 is provided therein with the brakedevice. These two brake devices can be used effectively, namely, onebrake device is for braking during running of the vehicle, and the otherfor a brake at the time of parking. With this structure, a mechanicallink interlocked with a running brake pedal and a mechanical linkinterlocked with a parking brake lever are distributed so as to besimplified. Moreover, the braking effect may be enhanced if both thefront and rear brake devices are connected to the running brake pedal soas to be actuated for braking simultaneously.

As shown in FIG. 8, a counter shaft 239 is arranged parallel to motorshaft 241, a wide, small diameter gear 217 fits loosely on counter shaft239, and a large diameter gear 216 is engaged on a toothed side of smalldiameter gear 217, thereby constituting a reduction-gear train 215.

Regarding reduction-gear train 215, large diameter gear 216 engages withdrive output gear 212, small diameter gear 217 engages with a ring gear221 of a differential gear unit 220, thereby transmitting the drivingforce from motor shaft 241 to differential gear unit 220 throughreduction-gear train 215.

Moreover, differential gear unit 220 comprises ring gear 221, whichengages with small diameter gear 217, pinions 223 rotatably supported byrespective pinion shafts 222 which project inward from an innerperiphery of ring gear 221, and left and right side gears 224 fixed torespective rear wheel axles 22L and 22R and engaged with each of pinions223. Due to this construction, the driving force of motor shaft 241 istransmitted to rear wheel axles 22L and 22R through reduction-gear train215, ring gear 221, pinions 223, and side gears 224.

Description will now be given of a hydraulic circuit structure inside ofcenter section 260 and a manifold block 268, which is attached to theundersurface of center section 260.

First, a first embodiment of a hydraulic circuit structure is described.According to the first embodiment, hydraulic motor 40 in front transaxleapparatus 10 and hydraulic motor 240 in rear transaxle apparatus 20 arefluidly connected in series to hydraulic pump in 230.

As shown in FIG. 8, into pump mounting surface 260 p in the horizontalportion of center section 260 are bored a first kidney-port 261 a and asecond kidney-port 261 b opposite to each other. These kidney-ports 261a and 261 b are open at a position above which openings of the cylinderbores of cylinder block 233 pass.

As shown in FIG. 10, into motor mounting surface 260 m in the verticalportion of center section 260 are bored a first kidney-port 262 a and asecond kidney-port 262 b opposite to each other. These kidney-ports 262a and 262 b are open at a position where openings of the cylinder boresof cylinder block 243 pass leftward.

As shown in FIGS. 9 to 11, in center section 260 are bored an upperfirst fluid passage 271 and a lower second fluid passage 272 parallel toeach other in the longitudinal direction of center section 260. Firstfluid passage 271 connects first kidney-port 261 a at pump mountingsurface 260 p to first kidney-port 262 a at motor mounting surface 260m. Second fluid passage 272 is connected at the front end thereof tosecond kidney-port 262 b at motor mounting surface 260 m.

Moreover, as shown in FIGS. 9 and 10, manifold block 268 is attached tothe undersurface of center section 260. In manifold block 268 from aside surface thereof are bored a third fluid passage 273 and a fourthfluid passage 274 parallel to each other and perpendicular to first andsecond fluid passages 271 and 272. Into openings of third and fourthfluid passages on the left side surface of manifold block 268 are fittedrespective caps 283 and 284 so as to constitute connection ports 273 aand 274 a. As shown in FIG. 9, ends of caps 283 and 284 project outwardfrom lower housing half 247 so as to be connected to hydraulic hoses(not shown) outside of lower housing half 247. The axes of connectionports 273 a and 274 a are disposed in a substantially horizontal plane,namely, they are not slant upward or downward, thereby facilitating theconnection work of piping comparatively. That is, the arrangement ofconnection ports 273 a and 274 a in the horizontal plane solves theproblems of the reduction of the ground clearance in the case of pipingwith downward ports and interference of piping with a transmission beltor a frame in the case of piping with upward ports.

Moreover, as shown in FIG. 9, between center section 260 and manifoldblock 268 are bored a vertical fifth fluid passage 275, which connectssecond fluid passage 272 to third fluid passage 273, and a verticalsixth fluid passage 276, which connects second kidney port 262 b in pumpmounting surface 260 p to fourth fluid passage 274.

Incidentally, a bypass operation lever (not shown) for opening firstfluid passage 271 and second fluid passage 272 to the fluid sump isdisposed at rear transaxle apparatus 20 in order to enable axles 22L and22R to idle when the vehicle is towed.

Due to the above-mentioned fluid passages, the hydraulic motor in thefront transaxle apparatus 10 and the hydraulic motor 240 in the reartransaxle apparatus 20 are fluidly connected in series to the hydraulicpump 230 in the rear transaxle apparatus 20.

That is, as shown in FIG. 2, hydraulic hose 81 a connects cap 54 a onthe front transaxle apparatus 10 to cap 283 on rear transaxle apparatus20, and hydraulic hose 81 b connects cap 54 b on front transaxleapparatus 10 to cap 284 on rear transaxle apparatus 20, thereby forminga hydraulic circuit shown in FIG. 12. The kind of fluid communicationmeans between the front and rear transaxle apparatuses 10 and 20 is notlimited. However, like hoses 81 a and 81 b according to this embodiment,the means is preferably flexible and resistant to considerably highpressure so as not interfere with the bending of the vehicle body.

According to the hydraulic circuit shown in 12, in center section 260arranged in rear transaxle apparatus 20, first kidney-port 261 a ofpump-mounting-surface 260 p is connected through first fluid passage 271to first kidney-port 262 a of motor mounting surface 260 m. Also, secondkidney-port 262 b in center section 260 of motor mounting surface 260 mis connected to first kidney-port 62 a in center section 62 of fronttransaxle apparatus 10 to motor mounting surface 63 m through a stringof fluid passages 299 a which consists of second fluid passage 272,fifth fluid passage 275, third fluid passage 273, hydraulic hose 81 a,and first fluid passage 53 a provided in center section 62 of fronttransaxle apparatus 10.

Second kidney-port 62 b formed in center section 62 of front transaxleapparatus 10 to is connected to second kidney-port 261 b formed inpump-mounting-surface 260 p in center section 260 through second fluidpassage 53 b provided in center section 62, hydraulic hose 81 b, and astring of fluid passages 299 b which consists of fourth fluid passage274 and sixth fluid passage 276 in the rear transaxle apparatus 20.

As mentioned above, in the hydraulic circuit structure according to thefirst embodiment, hydraulic motors 40 and 240, which are arranged infront and rear transaxle apparatuses 10 and 20, respectively, arefluidly connected in series to hydraulic pump 230. This in seriesconnection form is suitable for an articulated vehicle in which couplingpart 50 serves as a turning center of the vehicle and is arranged at anequidistant position from both the front and rear axles of the vehicle.

In this way, in front transaxle apparatus 10 and rear transaxleapparatus 20 are driven front wheel axles 12L and 12R and rear wheelaxles 22L and 22R, respectively, thereby realizing a four-wheel-drivevehicle which is excellent in both steering performance and runningperformance over bad ground conditions.

Especially, a four-wheel-drive working vehicle provided with the inseries hydraulic connection has the capability of freeing its runningwheels from mud. For example, even if the vehicle travels in a swamp anda front wheel is stuck in mud, hydraulic fluid discharged from hydraulicpump 30 bypasses hydraulic motor 40 in front transaxle apparatus 10 soas to idle the unloaded front wheels, and then flows into hydraulicmotor 240 in rear transaxle apparatus 20 so as to drive the loaded rearwheels, whereby the vehicle can escape from the mud smoothly.

Alternatively, caps 283 and 284 may be connected mutually through ahydraulic hose bypassing hydraulic motor 40 so as to make arear-wheel-drive vehicle which drives with only the driving force ofhydraulic motor 240 in rear transaxle apparatus.

When the rotary speed (peripheral speed) of front wheel axles 12L and12R is substantially identical to that of rear wheel axles 22L and 22R,hydraulic motors 20 and 240 in respective front and rear transaxleapparatuses 10 and 20 preferably have the same displacement (amount ofdischarge). With this composition, the same reduction gears may beapplicable to both front and rear transaxle apparatuses 10 and 20. Ofcourse, hydraulic motors of different volume can also be applied in thiscase, however, the mechanical deceleration ratio of front transaxleapparatus must be different from that of rear transaxle apparatus so asto substantially equalize the rotary speed (peripheral speed) of frontwheel axles 12L and 12R with that of rear wheels axles 22L and 22R.

In addition, as shown in FIG. 13, front transaxle apparatus for drivingthe front wheels may be modified so that the tilt angle of swash plate44 c of hydraulic motor is adjustable and swash plate 44 c isinterlockingly connected to steering wheel 4 through a wire, a link, orsimilar structure so as to correlate the tilt angle of swash plate 44 cand the turning angle of steering wheel 4, thereby increasing the rotaryspeed of the front wheel axles.

This structure is particularly effective for improving steeringperformance of a vehicle having an Ackerman type steering device or achassis layout wherein a difference of rotary speed is generated betweenthe front wheels and the rear wheels at the time of left or rightturning, namely, coupling part 50 is not located equidistant from thefront and rear axles of the vehicle.

Thus, regarding vehicles having the front and rear transaxle apparatuseswith a layout wherein a difference of rotary speed is generated betweenthe front wheels and rear wheels at the time of turning, and fluidlyconnecting in series the hydraulic motors in both the transaxleapparatuses, steering performance can be improved by making thehydraulic motor which actuates steerable wheels (the front wheels)variable in displacement, and increasing the rotary speed of thishydraulic motor in correspondence to the angle of the steering wheel.

Moreover, in hydraulic circuit shown in FIGS. 12 and 13, bypass valves40 v and 240 v are provided to front and rear hydraulic motors 40 and240, respectively, so that the fluid passages are opened to the fluidsump by the above-mentioned bypass operation lever, thereby enablingtowage of the vehicle. Towing the vehicle can be achieved if at leastone of front and rear transaxle apparatuses 10 and 20 is provided witheither bypass valve 40 v or 240 v, respectively. However, according tothis embodiment, both front and rear transaxle apparatuses 10 and 20 areprovided with respective bypass valves 40 v and 240 v. Therefore, at thetime of assembling, extraction of air can be done from each transaxleapparatus and 20 comparatively easily. Moreover, the vehicle can betowed even in low-temperatures and with high consistency of hydraulicfluid, because hydraulic fluid discharged from each of the idlinghydraulic motors 40 and 240 is bypassed near motor 40 or 240 so as notto be considerably resistant to towage of the vehicle.

Description will now be given of a hydraulic circuit structure accordingto a second embodiment, wherein hydraulic motor 40 in front transaxleapparatus 10 and hydraulic motor 240 in rear transaxle apparatus 20 arefluidly connected in parallel to hydraulic pump 230.

As shown in FIG. 14, in a horizontal portion of a center section 360 arebored a first kidney-port 361 a and a second kidney-port 361 b oppositeto each other. These kidney-ports 361 a and 361 b are open at a positionwhere openings of the cylinder bores of cylinder block 233 pass.

On the other hand, as shown in FIG. 17, in the vertical portion of thecenter section 360 are bored a first kidney-port 362 a and a secondkidney-port 362 b opposite to each other. These kidney-ports 362 a and362 b are open at a position where openings of the cylinder bores ofcylinder block 243 pass.

As shown in FIGS. 15, 16, and 18, in the center section are bored anupper first fluid passage 371 and a lower second fluid passage 372parallel to each other in the longitudinal direction of center section360.

As shown in FIG. 15, in center section 360 is bored a third fluidpassage 373 perpendicular to first fluid passage 371 so as to beconnected to first fluid passage 371. An opening of third fluid passage373 on a side surface of the center section 360 is closed by a plug 373a.

As shown in FIG. 16, in center section 360 are bored a slant fourthfluid passage 374, which connects second kidney-port 361 b to secondfluid passage 372. An opening of fourth fluid passage 374 on the sideface of center section 360 is closed by a plug 374 a.

Moreover, as shown in FIGS. 15 to 17, a manifold block 368 is attachedto the undersurface of center section 360. From a side surface ofmanifold block 368 are bored a fifth fluid passage 375 and a sixth fluidpassage 376 forward and backward parallel to each other andperpendicular to first and second fluid passages 371 and 372. Caps 385and 386 are fitted into respective openings of fifth and sixth fluidpassages 375 and 376 so as to form respective connection ports 375 a and376 a. As shown in FIGS. 15 and 16, ends of caps 385 and 386 opposite tomanifold block 368 project outward from a lower housing half 347 so asto be connected to hydraulic hoses (not shown) outside lower housinghalf 347. Axes of connection ports 375 a and 376 a are disposed in asubstantially horizontal plane (i.e., a plane which is oriented neitherupward nor downward) so as to facilitate piping thereto.

Between center section and manifold block 368 are bored a verticalseventh fluid passage 377 (FIG. 15), which connects a junction pointbetween second and fourth fluid passages 372 and 374 to fifth fluidpassage 375, and a vertical eighth fluid passage 378 (FIG. 16), whichconnects third fluid passage 373 to sixth fluid passage 376.

Due to the above mentioned fluid passage structure, hydraulic motor 40in front transaxle apparatus 10 and hydraulic motor 240 in reartransaxle apparatus 20 are fluidly connected in parallel to thehydraulic pump 230.

That is, as shown in FIG. 2, cap 54 a provided in front transaxleapparatus is connected to cap 385 provided in rear transaxle apparatus20 through a hydraulic hose 81 a, and cap 54 b in front transaxleapparatus 10 to the cap 386 in rear transaxle apparatus 20 through ahydraulic hose 81 b, thereby forming a hydraulic circuit shown in FIG.19.

According to the hydraulic circuit shown in FIG. 19, in center section361 a arranged in rear transaxle apparatus 20, the first kidney-port361, formed to pump mounting surface 360 p, is connected through firstfluid passage 371 to first kidney-port 362 a and to motor mountingsurface 360 m. First kidney-port of 361 a, formed in center section 361a to pump mounting surface 360 p, is connected to first kidney-port 62a, formed to the motor mounting surface 63 m, through a string of fluidpassages 399 a, which branch from first fluid passage 371 (as shown inFIG. 19) and consist of third fluid passage 373, sixth fluid passage376, hydraulic hose 81 a, and first fluid passage 53 a provided incenter section 62 of front transaxle apparatus 10.

On the other hand, in the center section arranged in the rear transaxleapparatus, the second kidney-port 362 b formed to the motor mountingsurface 360 m is connected to the second kidney-port 361 b formed to thepump mounting surface 360 p through a string of fluid passage 399 bwhich consists of the second fluid passage 372 and fourth fluid passage374.

Moreover, since the fourth fluid passage 374 is connected to the seventhfluid passage 377, the second kidney-port of 361 b formed to the pumpmounting surface 360 p is connected to the second kidney-port 62 bformed to the motor mounting surface 63 m through a string of the fluidpassage 399 c which consists of the fourth fluid passage 374, theseventh fluid passage 377, and the fifth fluid passage 375 (as shown inFIG. 19), hydraulic hose 81 b, and second fluid passage 53 b provided incenter section 62 of front transaxle apparatus.

In this way, in the hydraulic circuit structure according to the secondembodiment, hydraulic motors 40 and 340 arranged in respective front andrear transaxle apparatuses 10 and 20 are fluidly connected in parallelto hydraulic pump 230. Particularly, in this parallel connectionstructure is suitable for a vehicle which turns left and right whilegenerating a difference in rotary speed between the front wheels and therear wheels.

Due to the above structure, in front transaxle apparatus and reartransaxle apparatus 10 are driven front wheel axles 12L and 12R and rearwheel axles 22L and 22R, respectively, thereby making a four-wheel-drivevehicle which excels in steering performance and running performanceover bad ground conditions.

Alternatively, although not shown, caps 385 and 386 may be plugged so asto make a rear-wheel-drive vehicle which drives with only the drivingforce of hydraulic motor 340 of rear transaxle apparatus 20.

Moreover, as shown in FIG. 19, the vehicle provided with the in parallelhydraulic connection structure may be modified by providing differentialgear units 120 and 220 in front and rear transaxle apparatuses 10 and 20with respective differential-lock devices 125 and 225 for restrictingdifferential rotation of right and left axles and by providing operationlevers for differential-lock devices 125 and 225 on the vehicle, so asto restrict the differential rotation of the axles when any of therunning wheels are stuck.

In the in parallel connection, hydraulic fluid is distributed betweenthe two hydraulic motors 40 and 340, whereby a larger amount ofhydraulic fluid flows to the lighter-loaded of the hydraulic motors 40and 340. For this reason, when a right front wheel actuated by hydraulicmotor 40 is stuck, for example, the vehicle becomes impossible to freebecause hydraulic fluid doesn't flow to hydraulic motor and the rearaxles aren't actuated; by operating differential-lock device 125, loadfor driving a left front wheel is applied to hydraulic motor 40 so as tosupply a suitable amount of hydraulic fluid to rear hydraulic motor 340so as to drive the rear wheels, thereby enabling the vehicle to befreed. Incidentally, in the case where differential-lock devices 125 and225 are provided to respective front and rear transaxle apparatuses 10and 20, a common differential-lock pedal may be provided for both thedifferential-lock devices so as to actuate the devices simultaneously,or two pedals may be separately provided for the respectivedifferential-lock devices.

Description will be given of a second embodiment of the working vehiclehaving rear transaxle apparatus 20.

As shown in FIG. 20, in the working vehicle according to the secondembodiment, a pair of left and right front transaxle apparatuses 400Land 400R are provided to front frame 11. Left and right front transaxleapparatuses 400L and 400R include respective front-wheel axles 412L and412R, and are fluidly connected to rear transaxle apparatus 20 through adistribution device 80, hydraulic hoses, etc.

As shown in FIG. 21, an upper housing half 446 and a lower housing half447 are joined to each other so as to form a housing of each of fronttransaxle apparatuses for incorporating a hydraulic motor. Left andright front transaxle apparatuses 400L and 400R share the same structureand are supported on front frame 11 through respective stays 19 a and 19b so as to orient front-wheel axles 412L and 412R opposite to eachother.

As shown in FIG. 22, each of the front transaxle apparatuses 400L and400R incorporates a hydraulic motor 440, which is fluidly connected tohydraulic pump 230 in rear transaxle apparatus 20 (not shown). Rotationof a motor shaft 441 of hydraulic motor 440 is output to the outside ofthe housing through each of front wheel axles 412L and 412R.

As shown in FIG. 22, into each of front transaxle apparatuses isintegrally assembled hydraulic motor 440, which is so constructed that acylinder block 443 is rotatably slidably mounted on a motor mountingsurface 463 m formed on a vertical portion of a center section 462. Aplurality of pistons 442 are reciprocally movably fitted into aplurality of cylinder bores in cylinder block 443 through respectivebiasing springs. The heads of pistons 442 abut against a fixed swashplate 444 which is fixedly sandwiched between upper housing half 446 andlower housing half 447. An opening 444 b is provided in the center offixed swash plate 444 so as to allow motor shaft 441 to passtherethrough.

So that motor shaft 441 may function as an output shaft, motor shaft 441is rotatably supported by a sealed bearing 445 which is sandwichedbetween upper housing half 446 and lower housing half 447, and is notrelatively rotatably engaged with cylinder block 443 so as to bedisposed horizontally on the rotary axis of cylinder block 443.

Thus, an axial piston type fixed displacement hydraulic motor isconstructed in each of front transaxle apparatuses.

Moreover, as shown in FIG. 22, a pair of first and second kidney-ports462 a and 462 b are formed in a vertical portion of center section 462from a motor mounting surfaces 463 m. A first fluid passage 453 a and asecond fluid passage 453 b are horizontally formed in center section 462so as to be fluidly connected to respective kidney-ports 462 a and 462b. First fluid passage 453 a and second fluid passage 453 b areconnected to respective caps 454 a and 454 b to be connected torespective hydraulic hoses. Thus, each of hydraulic motors is fluidlyconnected to the hydraulic pump 200 in rear transaxle apparatus throughthe hydraulic hoses (not shown).

Although not shown, a bypass operation lever for opening first fluidpassage 453 a and second fluid passage 453 b to the fluid sump isincluded with each front transaxle apparatuses so as to idle front wheelaxles 412L and 412R when the vehicle is towed.

As shown in FIG. 22, on an end portion of motor shaft 441 opposite tothe center section 462 is provided a drive output gear 431 in splinefitting, whereby drive output gear 431 rotates integrally with motorshaft 441. On a portion of drive output gear 431 toward center section462 is integrally formed a brake rotor 433 whose diameter is larger thanthat of drive output gear 431, so that rotating motor shaft 441 isbraked by pressing brake rotor 433 between brake pads 434 a and 434 b.

Moreover, as shown in FIG. 22, bearing 439 a and 439 b rotatably supportfront-wheel axle 412L (or 412R) in parallel to motor shaft 441. Adeceleration gear 421 is fixed onto front-wheel axle 412L (or 412R) andengages with drive output gear 431. The diameter of deceleration gear421 is larger than drive output gear 431 so as to reduce the rotaryspeed of motor shaft 441 greatly so as to enable each of front transaxleapparatuses to incorporate a hydraulic motor having a small capacity.

Alternatively, although not shown, instead of front-wheel axle 412L (or412R), upper and lower housing halves 446 and 447 may be formed on aside thereof opposite to the center section 462 with an opening on anaxial extension of motor shaft 441, and motor shaft 441 may be extendedthrough the opening to the outside of the housing so as to be fixed tofront wheel 13. In brief, motor shaft 441 may replace front wheel axle412L (or 412R).

As shown in FIG. 20, front transaxle apparatuses constructed asdescribed above are fluidly connected to rear transaxle apparatusthrough distribution device 80, hydraulic hoses, etc., so as to driverespective front-wheel axles 412L and 412R, thereby rotating left andright front wheels 13.

There are several types of fluidal connection between front transaxleapparatuses 400L and 400R and rear transaxle apparatus 20. These fluidalconnection types will be described as follows.

According to an embodiment shown in FIG. 23, employing rear transaxleapparatus according to the first embodiment (shown in FIGS. 8 to 11),hydraulic motor 240 of rear transaxle apparatus and a circuit, whichfluidly connects in parallel hydraulic motors 440 of both fronttransaxle apparatuses 400L and 400R to each other, are fluidly connectedin series to the hydraulic pump of rear transaxle apparatus.

Due to this structure, front-wheel axles 412L and 412 of front transaxleapparatuses can be driven differentially.

According to an embodiment shown in FIG. 24, employing a fluidalconnection similar to that of FIG. 23, both hydraulic motors 440 offront transaxle apparatuses 400L and 400R are variable displacementhydraulic motors having respective movable swash plates 444 c. Thisstructure is particularly effective for a vehicle having an Ackermantype steering device or chassis layout wherein a difference in rotaryspeed is generated between the front wheels and the rear wheels at thetime of turning of the vehicle, namely, that coupling part 50 is notlocated at an equidistant position from both front and rear axles,because a difference of rotary speed can be generated between front andrear wheels by adjusting movable swash plates 444 c so as to improvesteering performance of the vehicle.

According to an embodiment shown in FIG. 25, employing rear transaxleapparatus according to the first embodiment, hydraulic motor 240 of reartransaxle apparatus 20 and hydraulic motors 440 of both front transaxleapparatuses 400L and 400R are all fluidly connected in series tohydraulic pump 230 of transaxle apparatus 20. Moreover, both hydraulicmotors 440 of front transaxle apparatuses 400L and 400R are variabledisplacement hydraulic motors having respective movable swash plates 444c.

This structure is particularly effective for a vehicle having anAckerman type steering device or a chassis layout wherein a differencein rotary speed is generated between the front wheels and the rearwheels at the time of turning of the vehicle, namely, that coupling part50 is not located at an equidistant position from both front and rearaxles, because a difference in rotary speed can be generated betweenfront and rear wheels by adjusting movable swash plates 444 c so as toimprove steering performance of the vehicle.

According to a hydraulic circuit shown in FIG. 26, employing reartransaxle apparatus according to the second embodiment (shown in FIGS.14 to 18), hydraulic motor 340 of rear transaxle apparatus 20 andhydraulic motors 440 of both front transaxle apparatuses are all fluidlyconnected in parallel to hydraulic pump of rear transaxle apparatus.

Due to this structure, front-wheel axles 412L and 412 of front transaxleapparatuses can be driven differentially.

Moreover, the hydraulic circuit in rear transaxle apparatus 20 isfluidly connected to the hydraulic circuit of front transaxle 400L and400R apparatuses through a control valve 80 a. If any of front wheels 13is stuck, control valve 80 a stops the supply of hydraulic fluid tofront transaxle apparatuses 400L and 400R, and hydraulic motor 340rotates rear wheel axles 22L and 22R, whereby the vehicle is freed.Furthermore, differential-lock device 225 is provided to restrict thedifferential rotation of rear wheel axles 22L and 22R so as tocorrespond to the situation where one of rear wheels 23 is stuck.

According to an embodiment shown in FIG. 27, employing rear transaxleapparatus 20 according to the second embodiment, hydraulic motor 340 ofrear transaxle apparatus 20 and a circuit, which fluidly connects inseries hydraulic motors 440 of both front transaxle apparatuses 400L and400R to each other, are fluidly connected in parallel to hydraulic pumpof rear transaxle apparatus in parallel. Moreover, both hydraulic motorsof front transaxle apparatuses 400L and 400R are variable displacementhydraulic motors having respective movable swash plates 444 c.

This structure is particularly effective for a vehicle having anAckerman type steering device or a chassis layout wherein a differencein rotary speed is generated between the front wheels and the rearwheels at the time of turning of the vehicle, namely, that coupling part50 is not located at an equidistant position from both front and rearaxles, because a difference in rotary speed can be generated betweenfront and rear wheels by adjusting movable swash plates 444 c so as toimprove steering performance of the vehicle.

Description will now be given of a layout of front transaxleapparatuses.

As shown in FIG. 21, inner ends of front wheel axles 412L and 412R,which are opposite to respective front wheels 13, are inserted inrespective front transaxle apparatuses 400L and 400R.

Front transaxle apparatuses are supported on left and right sideportions of front frame 11 through stays 19 a and 19 b, respectively, soas to ensure a lateral interval 401L between both front transaxleapparatuses 400L and 400R.

This interval 401L is wider than a lateral width 402L of secondworking-device drive transmission belt 59 at the position where belt 59passes front transaxle apparatuses.

With arranging front transaxle apparatuses 400L and 400R as describedabove, even if a working device such as mower device 3 is raised so asto change the vertical height where second working-device drivetransmission belt 59 passes, second working-device drive transmissionbelt 59 interferes with neither front wheel axles 412L and 412R norfront transaxle apparatuses. Therefore, the problem of secondworking-device actuation transmission belt 59 rubbing against frontwheel axle 412L, 412R, etc., and wearing out is not generated.

Three embodiments of FIGS. 28 to 30 will be described. First, a commonstructure among the three embodiments will be described. While separatefront transaxles 400L and 400R incorporating respecting hydraulic motors440 (either fixed displacement hydraulic motors 440 or variabledisplacement hydraulic motors 440) for driving respective axles 412L and412R are provided advantageously for passing a transmission mechanism(e.g., a belt transmission) to a working device (e.g., a mower unit)therebetween, a pump housing 500 incorporating hydraulic pump 230 isseparated from a housing of a rear transaxle 600 incorporating ahydraulic motor (either fixed displacement hydraulic motor 240 or avariable displacement hydraulic motor 640) for driving rear axles 22Land 22R.

One suction-and-delivery port of hydraulic motor 240 or 640 in reartransaxle 600 is fluidly connected to one suction-and-delivery port ofhydraulic pump 230 in pump housing 500, the other suction-and-deliveryport of hydraulic pump 230 is fluidly connected to both hydraulic motors440 in parallel, and the other suction-and-delivery port of hydraulicmotor 240 or 640 is fluidly connected to both hydraulic motors 440 inparallel. In this way, hydraulic motor 240 or 640 and the pair ofhydraulic motors 440 are fluidly connected in series to hydraulic pump230, and hydraulic motors 440 are fluidly connected in parallel tohydraulic pump 230, thereby constituting an HST closed circuit.

Input shaft 231 of hydraulic pump 230 projects outward from pump housing500 so as to be drivingly connected to engine 5 through belt 92. In pumphousing 500, a charge pump 501 is driven together with hydraulic pump230 by rotation of input shaft 231, so as to supply fluid to the HSTfluid circuit through either of a pair of charge check valves 502. Astop valve 503 bypasses hydraulic pump 230 between both thesuction-and-delivery ports of hydraulic pump 230, so as to be able todrain fluid from hydraulic pump 230 to the fluid sump in pump housing500. A relief valve 504 is disposed in pump housing 500 so as toregulate the pressure of fluid charged from charge pump 501.

In a housing of each of front transaxles 400L and 400R, axial pistontype hydraulic motor 440 with a center section (similar to that shown inFIG. 22) is disposed, and a deceleration gear unit 470 is interposedbetween hydraulic motor 440 and a corresponding front axle (471 or 472)whose outer end is connected to each front wheel 13. Deceleration gearunit 470 is a double planetary gear unit.

An external fluid reservoir tank 700 is fluidly connected to therespective fluid sumps of pump housing 500, rear transaxle 600 and leftand right front transaxles 400L and 400R, so as to absorb excessivefluid from the respective fluid sumps. Further, fluid reservoir tank 700is fluidly connected to charge pump 501 in pump housing 500 through aline filter 701 so as to supply fluid to charge pump 501.

Different points among the three embodiments of FIGS. 28 to 30 will bedescribed. Each of the vehicles of FIGS. 28 and 29 is an articulatedvehicle in which front transaxles 400L and 400R are secured onto frontframe 11, and rear transaxle 600 is secured onto rear frame 21. Anoutput shaft of deceleration gear unit 470 in each of front transaxles400L and 400R serves as axle 471 whose outer end is fixed to each frontwheel 13.

In the vehicle of FIG. 28, fixed displacement hydraulic motor 240 fordriving rear axles 22L and 22R is disposed in rear transaxle 600, andhydraulic motors 440 in respective front transaxles 400L and 400R arefixed in displacement. The vehicle of FIG. 28 includes vertical pivot 55articulately connecting front frame 11 and rear frame 21 (see FIGS. 1and 2), which is disposed at the fore-and-aft middle position betweenfront axles 471 and rear axles 22L and 22R, so that the equality ofrotary speed between front wheels 13 and rear wheels 23 is kept duringturning of the vehicle, thereby requiring neither acceleration nordeceleration of front or rear wheels 13 or 23 during turning of thevehicle. This is the reason why all hydraulic motors 240 and 440 arefixed in displacement.

With respect to the vehicle of FIG. 29, a difference of speed betweenfront wheels 13 and rear wheels 23 occurs during turning of the vehicle,because the vehicle of FIG. 29 is an articulated vehicle whose verticalpivot 55 is eccentric in the fore-and-aft direction toward either frontaxles 471 or rear axles 22L and 22R. Either the hydraulic motor in reartransaxle 600 or hydraulic motors 440 in respective front transaxles400L and 400R have to be accelerated or decelerated during turning ofthe vehicle.

Therefore, in the vehicle of FIG. 29, while hydraulic motors 440 inrespective front transaxles 400L and 400R are fixed in displacement,variable displacement hydraulic motor 640 for driving axles 22L and 22Ris disposed in rear transaxle 600 and provided with a movable swashplate 670 operatively connected to steering wheel 4, so that, accordingto left or right turning of steering wheel 4, the displacement ofhydraulic motor 640 is changed to decelerate or accelerate axles 22L and22R. Alternatively, in the articulated vehicle, fixed displacementhydraulic motors 240 may be disposed in rear transaxle 600, andhydraulic motors 440 of front transaxles 400L and 400R may be variablein displacement and provided with respective movable swash platesoperatively connected to steering wheel 4.

With respect to the vehicle of FIG. 30, a difference of speed betweenfront wheels 13 and rear wheels 23 also occurs during turning of thevehicle, because the vehicle of FIG. 30 is an Ackerman type steeringvehicle in which each of front wheels 13 is steerably (turnably)connected to an outer end of axle 472 serving as an output shaft ofdeceleration gear unit 470 in each of front transaxles 400L and 400R.

Therefore, in the vehicle of FIG. 30, while fixed displacement hydraulicmotor 240 for driving axles 22L and 22R is disposed in rear transaxle600, variable displacement hydraulic motors 440 are disposed inrespective front transaxles 400L and 400R and provided with respectivemovable swash plate 444 c operatively connected to steering wheel 4, sothat, according to left or right turning of steering wheel 4, thedisplacements of hydraulic motors 440 are changed to decelerate oraccelerate axles 472. Alternatively, in the Ackerman type steeringvehicle, variable displacement hydraulic motor 640 may be disposed inrear transaxle 600 and provided with a movable swash plate operativelyconnected to steering wheel 4, and hydraulic motors 440 of fronttransaxles 400L and 400R may be fixed in displacement.

In this way, with respect to the embodiments of FIGS. 29 and 30, theequality of rotary speed between rear wheels 23 and front wheels 13during turning of the vehicle is kept by acceleration or deceleration offront wheels 13 or rear wheels 23, thereby preventing front or rearwheels 13 or 23 from being dragged.

1. A vehicle comprising: a pair of first axles; a first transaxleincluding a single first transaxle housing incorporating a differentialfor differentially connecting the pair of first axles and incorporatinga first hydraulic motor for driving the differential, the firsthydraulic motor including suction and delivery ports; a pair of secondaxles; a pair of second transaxles including a pair of respective secondtransaxle housings separated from each other, and supporting therespective second axles, and a pair of respective second hydraulicmotors disposed in the respective second transaxle housings so as todrive the respective second axles, each of the second hydraulic motorsincluding suction and delivery ports; a hydraulic pump having suctionand delivery ports for supplying fluid to the first hydraulic motor andthe pair of second hydraulic motors; a parallel circuit including afirst line extended to connect the suction ports of the second hydraulicmotors to each other; and a second line extended to connect the deliveryports of the second hydraulic motors to each other; and a series circuitincluding a third line extended from one of the suction and deliveryports of the hydraulic pump and connected to one of the first and secondlines, a fourth line extended from the other of the suction and deliveryports of the hydraulic pump and connected to one of the suction anddelivery ports of the first hydraulic motor, and a fifth line extendedfrom the other of the suction and delivery ports of the first hydraulicmotor and connected to the other of the first and second lines, wherebythe series circuit fluidly connects the first hydraulic motor and theparallel circuit to the hydraulic pump in series, whereby the seriescircuit supplies fluid from the delivery port of the hydraulic pump viaone of the third and fourth lines to one of the first hydraulic motorand parallel circuit, and then supplies the fluid via the fifth line tothe other of the first hydraulic motor and parallel circuit beforereturning the fluid to the suction port of the hydraulic pump via theother of the third and fourth lines, and whereby the parallel circuitdistributes fluid from the series circuit via the first line to both thesuction ports of the second hydraulic motors in parallel, and collectsthe fluid from the delivery ports of the second hydraulic motors via thesecond line before returning the fluid from the second line to theseries circuit.
 2. The vehicle according to claim 1, wherein each of thesecond hydraulic motors has a variable displacement and has adisplacement control member for controlling the displacement, andwherein acceleration or deceleration of the second axles during turningof the vehicle by operative connection of the displacement controlmembers of the second hydraulic motors to a steering operation devicemakes a rotation speed of wheels connected to the second axles differentfrom a rotation speed of wheels connected to the first axles so as toprevent the wheels connected to the first axles and the wheels connectedto the second axles from dragging during turning of the vehicle.
 3. Thevehicle according to claim 1, wherein the first hydraulic motor has avariable displacement and has a displacement control member forcontrolling the displacement, and wherein acceleration or decelerationof the first axles during turning of the vehicle by operative connectionof the displacement control member of the first hydraulic motor to asteering operation device makes a rotation speed of wheels connected tothe first axles different from a rotation speed of wheels connected tothe second axles so as to prevent the wheels connected to the firstaxles and the wheels connected to the second axles from dragging duringturning of the vehicle.